Internal gear pumps are known and have long been used for the pumping of thin liquids at relatively high speeds. The typical internal gear pump design includes a rotor mounted to a drive shaft. The rotor includes a plurality of circumferentially disposed and spaced apart rotor teeth that extend axially toward an open end of the pump casing. The open end of the pump casing is typically covered by a head plate or cover plate which, in turn, is connected to an idler. The idler is eccentrically mounted to the head plate with respect to the rotor teeth. The idler also includes a plurality of spaced apart idler teeth disposed between alternating idler roots. The idler teeth are tapered as they extend radially outward and each idler tooth is received between two adjacent rotor teeth. The rotor teeth, in contrast, are tapered as they extend radially inward. A crescent or sealing wall is disposed below the idler and within the rotor teeth. The crescent provides a seal to prevent the loss of fluid disposed between the idler teeth as the idler teeth rotate. The rotor teeth extend below the crescent before rotating around to receive an idler tooth between two adjacent rotor teeth.
The input and output ports for internal gear pumps are disposed on opposing sides of the rotor. The fluid being pumped is primarily carried from the input port to the output port to the space or roots disposed between adjacent idler teeth. This space may be loaded in two ways: radially and axially. The space is loaded radially when fluid passes between adjacent rotor teeth before being received in a root disposed between adjacent idler teeth. Further, there is typically a gap between the distal ends of the rotor teeth and the head plate or casing cover which permits migration of fluid from the inlet port to an area disposed between the head plate and the idler. After migrating into this area, the fluid can be sucked into the area or root disposed between adjacent idler teeth during rotation of the idler and rotor.
However, it has been found that it is very difficult to ensure a complete loading of the innermost area between the idler teeth or the root disposed between adjacent idler teeth. The failure to provide a complete loading of this area results in an inefficiency of the pump. Therefore, there is a need for a way to improve the loading of the idler roots or the loading of internal gear pumps as a means for improving efficiencies.
Another problem commonly associated with internal gear pumps is the difficulty in assembling these pumps. Specifically, a seal is needed between the rotor and the bearing assembly or the outboard end of the drive shaft. Because the rotor is typically fixedly connected to the drive shaft, the drive shaft must be passed through the pump chamber and casing during an initial installation step. Then, from an opposing end of the casing, a seal assembly must be inserted over the outboard end of the drive shaft and pushed into place in the casing between the motor housing and the pump chamber. Because the shaft is already in place, the seal assembly must be installed blindly or without being able to view the seal assembly or the section of shaft upon which it is installed during installation thereof. As a result, the installation of the seal assembly is time consuming and the seal assembly can often be damaged during installation. Further, the seal assemblies are susceptible to being installed incorrectly, which is not detected until the pump is tested
Therefore, there is a need for an improved internal gear pump design which facilitates the assembly of the pump and, more specifically, the installation of the seal assemblies over the drive shafts.